The benefits of regular exercise are well known and recently there has been considerable evolution in exercise products which are resistive in nature and designed to improve one's cardiopulmonary endurance. Initially, exercise bikes were developed which gave the user a plain circular pedal path that mimicked road cycling. Cross country ski machines have provided linear reciprocating paths. Steppers have mimicked the motion of climbing stairs with oscillatory pedals. Lately, there has been a trend toward more complicated motions that move a pedal in a generally elliptical curved path and attempt to mimic walking or jogging.
These elliptical machines have themselves evolved over time and come in many configurations. As the elliptical machines have evolved, several strategies have been developed to improve the biomechanics of the path of the pedal.
U.S. Pat. No. 5,383,829 to Miller; U.S. Pat. No. 5,685,804 to Whan-Tong et al.; U.S. Pat. No. 6,482,130 to Pasero et al.; and U.S. Pat. No. 6,146,313 to Whan-Tong et al. describe various versions of an exercise machine that produce elliptical motion at the foot placement or pedals by using a large crank attached to one end of a foot supporting member and either a rolling element or a swinging rocker at the other end to guide the foot supporting member along a reciprocating path. The pedal path may be adjusted in various ways resulting in the angle of the ellipse major axis being more steeply inclined.
The problem with these designs is twofold. Due to the circular path of the crank, the ratio of ellipse major axis to minor axis is smaller when compared to the normal walking stride of an individual and, as a consequence, not optimal for biomechanics. This is to say that the ellipse height is too deep in relation to the length. The second problem is in the nature of the ellipse. Due to the simple crank-rocker or crank-slider type linkage, there is a great deal of angular change in the vicinity of direction changes. This tends to feel abrupt for many people and results in the foot being angled upward as the foot travels back in the stride.
U.S. Pat. Nos. 5,957,814, 6,168,552 and 6,440,042 to Eschenbach describe a unit consisting of a crank, various linkage elements, a pair of pedal members and a guide upon which rolls the ends of each pedal member. The guide is adjustable in order to change the pedal paths.
U.S. Pat. Nos. 5,997,445 and 6,248,044 to Steams and Maresh describe devices that use a rocker linkage to provide elliptical motion at the end of a pedal link which is guided in the middle with the user standing on a pair of pedals which are cantilevered at the rear. The guide means may take the form of a rolling member or a linkage member. The guide means for the rolling member may be adjusted to change the pedal path. It should be noted that this configuration produces a motion at the pedal link joint (designated as P1 in FIG. 2 and 3 of U.S. Pat. No. 5,997,445) which is purely elliptical in shape as shown and described in the art.
U.S. Pat No. 5,895,339 to Maresh describes another exercise device that utilizes a crank and rocker arrangement to generate an elliptical path.
U.S Pat. No. 5,792,026 to Maresh and Steams describes a device that utilizes a crank and drawbar mechanism to elongate the pedal path.
The defining point in the majority of the prior art is in developing a mechanism which converts the circular motion of a crank into a substantially elliptical path occurring at the pivot point where the link member or pedal arm is attached. This is done to maximize the length of the stride while at the same time keeping the height within reasonable limits for proper biomechanics. The shape of the travel path of this pivot point is a key element in providing a normal stride feel to the user.
Indeed, due to an individual's biomechanics and preferences, there becomes a need for a means to alter the shape or size of the pivot point travel path in order to accommodate the preferences of a variety of users.